The present invention broadly relates to a clutch device or arrangement for a power transmission and, more specifically, pertains to a new and improved construction of a clutch device or arrangement for marine vessel power transmission units having at least two switchable, i.e. engageable and disengageable jaw or toothed clutches disposed in parallel power transmission paths and a converter or actuating mechanism, wherein one of the clutches is a main self-engaging clutch having a synchronizing device and at least one further clutch is a subsidiary clutch without a synchronizing device. The converter translates the engaging motion of the main clutch into an engaging motion of the subsidiary clutch.
Clutch arrangements of this type are mainly employed in so-called locked-train transmissions, i.e. transmissions having multiple power paths and in which a drive pinion meshes with gear wheels on parallel intermediate or counter shafts each driving an intermediate pinion through switchable jaw or toothed clutches and the intermediate pinions mesh with a common main or large drive gear. Such transmission units are used, for instance, in marine vessels with multiple engine drive to couple a gas turbine with the propeller shaft or uncouple it according to requirements. In comparison to other power transmissions with multiple power paths and only one engageable clutch disposed ahead of the drive pinion, power transmissions of the type described have the advantage that the first transmission or reduction stage of the gear set comprising the drive pinion and the intermediate gears meshing with it is also taken out of operation when the associated engine, for instance gas turbine, is disconnected by disengaging the engageable jaw or toothed clutches. This has the result that only the second transmission or reduction gear stage comprising the intermediate pinions and the main drive gear meshing with them are maintained in motion by a further rotation of the driven or power output shaft, for instance propeller shaft.
When engaging the jaw or toothed clutches of a clutch arrangement of the type described, care must be taken that the main clutch not be subjected to a torque load, or be subjected to only a minimal torque, as long as the subsidiary clutch is not engaged. A premature loading of the main clutch would torsionally stress the associated intermediate shaft producing a misalignment of the clutch teeth or splines of the subsidiary clutch and consequently preventing trouble-free engagement. It must on the other hand also be avoided that the subsidiary clutch be subjected to appreciable torque loading before it is fully engaged, since such loading could give rise to frictional resistance forces between the clutch teeth or splines of the subsidiary clutch which overload the converter or actuating mechanism causing it to distort and possibly block if it is, for instance, a lever or bar linkage.
In known clutch arrangements of the type described a helically toothed or splined coupling sleeve forms one half of each jaw or toothed clutch. The coupling sleeve engages an intermediate or counter shaft by means of helical teeth or splines. Significant in this respect are British Pat. No. 1,076,273, published July 19, 1967, German Pat. No. 2,900,414, published Sept. 17, 1970, and European Pat. No. 0 002 888, published July 11, 1979. This coupling sleeve has straight teeth or splines which can engage with complementary straight teeth or splines of a second clutch half. The synchronizing device of the main clutch comprises pawls mounted on the helically splined or toothed coupling sleeve and cooperating with either the straight toothed spline or teeth of the other jaw or toothed clutch half or special ratchet teeth. Significant in this respect are further the aforementioned British Pat. No. 1,076,273, FIG. 6 and German Pat. No. 2,900,414. When the pawls transmit a torque from one half of the clutch to the other, the helical spline or screw thread between the coupling sleeve and its associated intermediate shaft converts it into an axial force which displaces the coupling sleeve, thus engaging the clutch splines or teeth and disengaging the pawls. In order to unload the pawls, the main clutch has helical entry teeth which engage in advance of the clutch teeth proper to effect the full engagement in place of the pawls. The entry teeth finally disengage again. Significant in this respect is the aforementioned German Pat. No. 2,900,414, FIG. 3a.
In known designs, the converter or actuating mechanism is formed by a two-armed or rocking lever having a claw at each end which fits into a ring groove in each of the coupling sleeves with considerable axial play. The purpose of the play is to assure that the synchronizing device of the main clutch first moves only the main clutch in the axial direction until the entry teeth engage. Then further axial motion brings the subsidiary clutch or clutches into engagement. Then their helically-splined coupling sleeves begin to generate sufficient axial force to complete the engagement. The purpose of this arrangement is to relieve the main clutch of the load of shifting the helically-splined coupling sleeve of the subsidiary clutch or clutches. It was heretofore believed that considerable play between the clutch splines or teeth of the subsidiary clutch was essential. This has the result that the main clutch begins to transmit a torque force before the subsidiary clutch. In order to avoid that the main clutch carries considerably more load than the subsidiary clutch as a result of this teeth clearance or play of the subsidiary clutch when both clutches are engaged, in one of the constructions described in the aforementioned European Pat. No. 0 002 888 the main clutch is disposed in a force transmission path whose torsional resistance is considerably less than that of the force transmission path in which the subsidiary clutch is disposed.
The excessive tooth clearance provided and considered essential in heretofore known constructions gives rise to disturbing noises (tooth pounding) when rotational oscillations occur in the transmission. Such oscillations cannot always be avoided in marine transmissions. Producing a locked-train power transmission with intermediate or counter shafts of differing torsional rigidity or stiffness involves considerable additional expense in comparison to a design with fully identical intermediate or counter shafts. Finally, in known clutch or coupling arrangements of the type described it can hardly be avoided that the pawls provided for the synchronization of the main clutch are heavily loaded when unfavorable conditions of operation coincide. This can lead to damage to the pawl and ratchet drive with the possible consequence that the main clutch and therefore also the subsidiary clutch can no longer be engaged.